Prenatal diagnosis has been routinely conducted using cells isolated from the fetus through procedures such as chorionic villus sampling (CVS) or amniocentesis. These conventional methods are, however, invasive and present an appreciable risk to both the mother and the fetus despite most careful handling (Tabor et al., Lancet 1:1287-1293, 1986).
Alternatives to these invasive approaches have been developed for prenatal screening, e.g., to detecting fetal abnormalities, following the discoveries that several types of fetal cells can be found in maternal circulation (Johansen et al., Prenat. Diagn. 15:921-931, 1995) and more importantly, circulating cell-free fetal DNA can be detected in maternal plasma and serum (Lo et al., Lancet 350:485-487, 1997). The amount of fetal DNA in maternal blood has been shown to be sufficient for genetic analysis without complex treatment of the plasma or serum, in contrast to the necessary steps for isolating and enriching fetal cells. Fetal rhesus D (RhD) genotyping (Lo et al., N. Engl. J. Med. 339:1734-1738, 1998), fetal sex determination (Lo et al., Hum. Genet. 90:483-488, 1993), and diagnosis of several fetal disorders (Amicucci et al., Clin. Chem. 46:301-302, 2000; Saito et al., Lancet 356:1170, 2000; and Chiu et al., Lancet 360:998-1000, 2002) have since been achieved by detecting fetal DNA in maternal blood using a polymerase chain reaction (PCR)-based technique.
In addition, quantitative abnormalities of fetal DNA in maternal plasma/serum have also been reported in preeclampsia (Lo et al., Clin. Chem. 45:184-188, 1999 and Zhong et al., Am. J. Obstet. Gynecol. 184:414-419, 2001), fetal trisomy 21 (Lo et al., Clin. Chem. 45:1747-1751, 1999 and Zhong et al. Prenat. Diagn. 20:795-798, 2000) and hyperemesis gravidarum (Sekizawa et al., Clin. Chem. 47:2164-2165, 2001). Detection of fetal nucleic acid in maternal blood for prenatal genetic analysis is also disclosed in U.S. Pat. No. 6,258,540.
When analyzing fetal DNA, investigators have often used Y chromosomal markers, which are only present in male fetuses, as a fetal-specific marker. This approach has limited the application of this technology to the 50% of pregnant women who are carrying male fetuses. Further, the use of other genetic polymorphisms has also increased the complexity of fetal DNA-based analyses. The discovery of fetal RNA in maternal plasma offers a possible new approach that circumvents these limitations (Poon et al., Clin. Chem. 46:1832-1834, 2000).
More recently, U.S. patent application Ser. No. 09/876,005 discloses non-invasive techniques based on detection of fetal/placental RNA in maternal blood. Further, U.S. patent application Ser. No. 10/759,783 discloses certain placental expressed mRNA markers (e.g., human chorionic gonadotropin β subunit and human corticotropin releasing hormone) that can be used for the detection of pregnancy and pregnancy-related disorders such as preeclampsia, fetal chromosomal aneuploidy, and pre-term labor. Various other RNA species of placental origin have also been detected in maternal blood, see, e.g., Oudejans et al., Clin Chem. 2003, 49(9):1445-1449, and Go et al., Clin. Chem. 2004, 50(8):1413-1414. The present invention discloses additional fetal/placenta-derived RNA species, shown in Tables 1-6, that are found in maternal blood and can be used as markers for detecting pregnancy, or for genotyping the fetus, or for diagnosing, monitoring, and predicting preeclampsia and fetal chromosomal aneuploidy such as trisomy 18 and trisomy 21. Thus, the present invention provides additional tools for non-invasive prenatal diagnosis and alternative means for pregnancy detection.